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Polyethylenimine (PEI) and plasmid DNA (pDNA) complexes (PEI/pDNA) are nonviral vectors for gene delivery. The conventional method for producing these complexes involves bulk mixing (BM) of PEI and DNA followed by vortexing which at low N/P ratios results in large particle size distribution, low cytotoxicity, and poor gene transfection, while at high N/P ratios it results in small particle size and better gene transfection but high cytotoxicity. To improve size control, gene transfection efficiency, and cytotoxicity, in this study, we used a microfluidic hydrodynamic focusing (MF) device to prepare PEI/pDNA complexes at N/P = 3.3 and 6.7. We used bulk mixing as control, mouse NIH 3T3 fibroblast cells and mouse embryonic stem (mES) cells as model cell lines, plasmid encoding green fluorescent protein (pGFP) and secreted alkaline phosphatase (pSEAP) as the reporter gene, and commercially available Lipofectamine 2,000 as a positive control. The complexes were characterized by atomic force microscopy (AFM), dynamic light scattering (DLS), and zeta potential (zeta) measurement. Confocal laser scanning microscopy (CLSM) and fluorescent labeling techniques were used to visualize the complex size distribution, complexation uniformity, and cellular distribution. The results showed that MF produced complexes were smaller and more uniformly complexed and had higher cell viability and improved exogenous gene expression.
Koh et al. (Thu,) studied this question.